This may be an exercise in futility, but . . .
. . . I get the impression that there are certain whistles that are best exemplified, or enjoyed, in specific keys. I realize that some whistlemakers limit themselves to one or two keys. Any thoughts?
matt
I’ve always found that Colin Goldie seems to have special affinity for A, F, and low D. That said, I want all the other keys, too! 
I just got my first Chieftain Gold Mezzo A, and I really love the sound and playability. I am borrowing a Burke G Al pro, that is creamy smooth with a pure voice, and the easiest whistle I have played to move through the octaves. Both sound great to me, but definitely a different sound to each. I suppose as I learn more songs, I may find certain keys or songs where I want more chiff, or purity of sound?? Can’t say yet. But, any thoughts on the Burke low F and D. Do they sound as good as the G AL pro?
The whistles that really stand out to me arethe Thin Weasel C and Bflat. I’ve played a LOT of C’s and quite a few Bflats, and these simply blow all others out of the water.
The Grinter low-F is the stuff of which legends are made, but I like the low-G considerably more. That’s saying a lot.
I also like the Burke low-G. As you said, it’s just SOO easy to play; but it would be hard to pick it above the D WBB or the low-E.
Grinter low F
Copeland low D and G (if you manage to get great ones)
Abell high F (some great Abells around in all the old keys)
Sindt Eb (very good in all keys)
Overton low D, low F, low G and A (great Overtons in every key)
Burke AlPro low G and C (also very consistent across the range)
Busman D.